Oxygenator wedge configuration

ABSTRACT

A device (10) having a blood oxygenator (12) and heat exchanger (14) of the outside perfusion type. The blood oxygenator (12) employs a tightly packed, crisscrossing bundle of gas permeable hollow fibers (50). The heat exchanger (14) employs a bundle of polyurethane, liquid impermeable hollow tubes (96). A center divider (16) facilitates two separate compartments (30, 40) and allows control over pack densities within each compartment while allowing blood to move in a planar manner throught out the device (10).

FIELD OF THE INVENTION

This invention relates to a blood oxygenator of the outside perfusiontype using hollow-fiber membranes and to blood oxygenators havingcoextensive integral heat exchanging units. More particularly, theinvention relates to an improved apparatus and method of winding hollowfibers into a blood oxygenator unit.

DESCRIPTION OF THE PRIOR ART Blood Oxygenator

In known blood oxygenators, hollow fibers are used as a means to bringblood into contact with oxygen and provide a means for removal of carbondioxide from the blood. For simplicity, such gas exchange will bereferred to herein with regards to the oxygenation only, it beingunderstood that transfer of oxygen into and carbon dioxide out of theblood is taking place. The fibers are typically made of a homogeneousmembrane of gas-permeable material such as silicone or of hollow fibersmade of a microporous membrane of hydrophobic polymeric material such aspolyolefins

There are two types of hollow fiber blood oxygenators: the insideperfusion type in which blood is passed through the bores of the hollowfibers while oxygen is passed on the outside of the hollow fibers andthe outside perfusion type. Blood oxygenators of the outside perfusiontype pass oxygen through the bores of the hollow fibers while blood isflowed past the outside of the hollow fibers.

In blood oxygenators of the inside perfusion type, no channeling of theblood occurs provided the blood is uniformly distributed and fed to theinterior of the large number of hollow fibers involved. However, sincethe blood flowing through the bores of the hollow fibers moves in avirtually perfect laminar flow, the internal diameter of the hollowfibers needs to be reduced to a small diameter in order to increase theoxygenation rate (i.e., the oxygen transfer rate per unit volume ofblood per unit area of membrane).

The laminar flow phenomenon of the blood passing through the hollowfibers presents many problems even when very fine hollow fibers areused. The result is that the oxygenation rate of a blood oxygenator ofthe inside perfusion type is not as beneficial as might be expectedEffectiveness of oxygen transfer is in part determined by the surfacearea contact of the blood with hollow fiber. Obviously, a much largersurface area contact results when blood is on the outside of the hollowfiber than when the blood is internal to the fiber.

If the oxygen is not distributed uniformly into the blood, the carbondioxide desorption rate from the blood (i.e., the carbon dioxidetransfer rate out of the blood per unit volume of blood per unit area ofmembrane) will be reduced.

In the common configuration for inside perfusion blood oxygenators, acylindrical housing is simply packed with a large number of hollowfibers for gas exchange arranged so that the hollow fibers are parallelto the longitudinal axis of the cylindrical housing. Blood oxygenatorsof this construction have lower than desired gas exchange rate per unitarea of the hollow fiber membrane.

In contrast, in blood oxygenators of the outside perfusion type theoxygen can be distributed uniformly through the spaces between adjacentfibers and the blood can be expected to move with better mixing.However, outside perfusion has had the disadvantage of being subject toless than the desired oxygenation of the blood because of regionalchanneling of the blood as it passes transversely to the outsides of thehollow fibers.

The known outside perfusion type blood oxygenators in which the hollowfibers are in perpendicular orientation to the direction of blood flowproduces more mixing of the blood as the blood flows than insideperfusion constructions. This arrangement can bring about an improvementin oxygenation rate, as compared with those inside perfusion types orconstruction in which the hollow fibers are arranged to have theirlength parallel to the direction of blood flow. However, if the numberof fibers used in such a blood oxygenator is large (as is desirable)and/or the flow rate of blood is increased in order to treat largevolumes of blood, problems arise. For example, unacceptable pressuredrop of the blood between inlet and outlets and/or channeling of theblood between groups of fibers may occur. By channeling it is to beunderstood that a significant flow of blood takes place throughrelatively large area voids between fibers so that there is little or nomixing. As the rate of oxygen transfer primarily takes place in a thinboundary layer adjacent the hollow fibers, the effectiveness of desiredoxygenation is reduced.

Blood-side convective mixing is essential for efficient gas transfer inblood oxygenators. Without such mixing, sharply defined boundary layersof fully oxygenated blood develop near the exchange surfaces and thefluxes of oxygen and carbon dioxide tend to be low. Low transportefficiency results in bulky devices with undesirably high blood primingvolumes.

Other investigators have proposed constructions in attempts to reducethese problems. In U.S. Pat. No. to Takemura, Pat. No. 4,639,353, anoxygenator is shown in which a plurality of contact chambers areutilized each being limited in thickness as an attempt to discourage theundesired channeling.

Heat Exchanger

In prior art heat exchangers for blood oxygenator systems, the heatexchanger is typically made of a metal such as stainless steel tubing.Such materials are not as blood compatible as desired. Others have usedpolyethylene or polypropylene hollow fiber bundles in heat exchangers.However, potting compounds are less certain of seal than is desired. Itis mandatory that there be no leakage of the cooling fluid used in theheat exchanger to the blood. If water or other heat exchange medium wereto leak into the blood being treated, the impact to the patient could beserious.

SUMMARY OF THE INVENTION

The present invention provides blood oxygenators of the outsideperfusion type having high oxygen transfer rates, high carbon dioxidetransfer rates, efficient heat exchange, and a construction whichresults in little or no stagnation of blood. Channeling of the blood isminimized. The devices of the invention provide very good oxygenationperformance. As compared to prior devices having equal fiber surfacearea, the devices of the present invention provide superior oxygenation.Thus, a desired oxygenation rate may be achieved while using less totalquantities of the costly fibers.

When coupled with the heat exchanger of the invention, the unitarydevice results in a highly compact blood oxygenator capable of givingthe needed gas transfer and temperature control. A further advantage ofthe construction of the invention lies in the parallel planeconstruction of the oxygenator and heat exchanger sections coupled witha means to have an uninterrupted, substantially planar flow pattern ofblood transverse to both the oxygenator and heat exchanger without aninterruption.

The heat exchanger is of an outside perfusion type constructionutilizing a bundle of polyurethane hollow tubes. The large surface areaprovided for contact with the blood provides a very effective heatexchanger of the compact size even though polyurethane tube have a lowheat transfer coefficient compared to stainless steel. Polyurethanehollow tubes, unlike the polyolefin heat exchange fiber materialspreviously used, are completely compatible with urethane pottingcompounds used to encapsulate the ends of both the oxygenator hollowfibers and of the heat exchanger hollow tubes. Therefore, the heatexchanger built in accordance with this invention substantially removesthe possibility of leakage at the hollow fiber and hollow tube endpotting interface. Such a possiblity of leakage exists in the prior art.

The combination of oxygenator and heat exchanger provides an oxygenatorwhich, as designed, meets the Draft Standard For Blood/Gas ExchangeDevices (Oxygenators) of the Association for the Advancement of MedicalInstrumentation, February 1982 Revision. (Commonly referred to in theindustry as the A.A.M.I. Standards).

The devices of the invention are arranged and designed to be relativelysimple to construct, thereby lowering costs of manufacture over knownprior art units.

According to the present invention, there is provided a devicecomprising a blood oxygenator and an integral heat exchanger. A housingdivider-diffuser plate with perforations separates the blood oxygenatorhollow fiber bundle from the heat exchange hollow tube bundle. Accessmeans are provided so that blood enters the heat exchanger sectionthrough a port which opens into a first chamber extending coextensivewith the length and width of the heat exchange hollow tube bundle. Bloodentering the first chamber passes through a first perforated diffuserplate which acts to distribute blood evenly over the surface of the heatexchange hollow tubes and across the depth of the bundle of tubes.

The heated or cooled blood is then distributed, without beingrecollected to a bulk quantity, to a oxygenator bundle of hollow fibersby passage through the housing divider diffuser plate. The oxygenatorbundle of hollow fibers consists of tightly packed hollow fibers. Thefiber and the tube ends are all potted in potting compound in a singlestep at each end such that each fiber and tube extends between endpotting blocks. Strong mixing of the blood is induced on the blood sideof the fibers by the tortuous path that the blood must take in flowingpast the fibers of the bundle.

The hollow fibers are laid into the device such that the fibers crossover each immediately previously laid adjacent fiber at an angle ofbetween about 8 and about 25 degrees. At the completion of laying downone full layer of fibers across the housing-divider diffuser plate, thepattern of laying down is shifted slightly out of phase such that thenext layer of fibers cross the previously laid fibers adjacent fibers ata 8 to 25 degree angle but are shifted from the underlying layer. Thiscreates a relatively even pack density throughout the bundle, increasesthe tortuous blood path and therefore substantially reduces areas whereshunting and channeling may occur. However, in the preferred form of thepresent invention, the hollow fibers for the oxygenator portion are laiddown on a specially configured H-shaped member to further reduce thepossibility of undesired channeling.

The preferred angling of the fibers is at angles of about 9 from thesides of the housing. A pack density of about 50-55% of the availablecross-sectional area at the midpoint has been found to minimizechanneling and shunting without causing an unacceptable pressure drop. Alower packing density may be used within the potted ends of the fibersto facilitate fiber end encapsulation. A substantial drop in oxygentransfer is observed at a density of 45%. Channeling of blood flow isfound in devices packed at less than about 40%. When the pack density isgreater than about 55% the blood pressure drop between entering andleaving rises to unacceptable levels.

Blood, after traversing the oxygenation fibers, exits the oxygenatingbundle through a second perforated diffuser plate while retaining itsgenerally planar flow. The blood then passes out of the housing throughan outlet which may open transversely to the length of the oxygenatorfibers. Both of the perforated diffuser plates are spaced from theexterior housing and provide support to the fiber and heat exchangerbundles.

The required packing density of the oxygenator fibers and heat exchangetubes may be easily maintained by virtue of the three diffuser plates.By the special configurations of the present invention, improvements inseveral respects are provided over the use of simple rectangular,cross-sectional regions for laying down the hollow fibers. The diffuserplates with the chamber and cover define a predetermined rigidcross-sectional area for the fibers and tubes.

The device is very compact which is an important feature of efficientoxygenators. The compactness may be achieved with a minimum of parts andmanufacturing steps.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description of the invention, including its preferredembodiment, is hereinafter described with specific reference being madeto the drawings in which:

FIG. 1 is an exploded pictorial view of the device of the invention;

FIG. 2 is a perspective view of the unexploded device of FIG. 1 from thereverse side;

FIG. 3 is a cross-section taken along line 3--3 of FIG. 2;

FIG. 4 is a top plan view of the device of FIG. 2 with portions cut awayto show the oxygenator fibers and diffuser plate;

FIG. 5 is a side plan of the device of FIG. 2;

FIG. 6 is a front plan view of the device of FIG. 2;

FIG. 7 is a photographic view of a partial first layer of oxygenationfibers within a core;

FIG. 8 is a partial cross-section taken along line 8--8 of FIG. 2.

FIG. 9 is a cross-sectional view of the preferred form of the inventionin cross-section showing the use of shaping members to produce thedesired packing density;

FIG. 10 is a perspective view of an insert member for use in theproviding of a shaping, and

FIG. 11 is a cross-sectional view on lines 11--11 of FIG. 10.

FIG. 12 is a graph showing the relationship of fiber pack density tooutlet partial pressure of oxygen in the blood oxygenator of theinvention.

FIG. 13 is a graph showing the relationship of pressure drop to fiberpack density through the oxygenator fiber bundle.

DETAILED DESCRIPTION OF THE INVENTION

The device generally marked 10 of FIGS. 1-6 comprises an oxygenationsection 12 and a heat exchanger section 14 which are separated by acommon center divider 16. Preferably, the casing and divider elementsare formed from biocompatible plastics capable of hermetically beingbonded by potting compounds of the urethane type.

Device 10 includes an elongated rigid core member 20 of generallyH-shaped cross-section which defines an upper channel shaped region 30and lower channel shaped region 40. Each channel region is alongitudinally extending groove in the core member. Center divider 16forms the web between the outside legs 42, 44 of the H of the coremember 20.

Oxygenator section 12 includes the area defined by upper channel 30.Channel 30 is filled with hollow fibers 50 arranged longitudinally suchthat the hollow fibers generally are oriented in the direction roughlyparallel to the legs 42, 44.

Each of the hollow fibers 50 is a membrane designed for gas exchange.Each hollow fiber may comprise a porous resin capable of gas transfersuch as polypropylene, polyethylene or other biocompatible suitablematerial which provides a gas exchange. The fibers are liquidimpermeable. Suitable fibers for this purpose are well known andcommercially available from a number of vendors including MitsubishiRayon Co., Ltd. of Tokyo, Japan and Celanese Chemical Co. of New York,New York.

A diffuser plate 60 as shown in FIGS. 1, 3, and 4 covers the upper layerof hollow fibers 50 and is attached to legs 42, 44 along its side edges.Diffuser plate 60 includes a plurality of orifices 62 which are spacedthroughout the plate 60. Orifices 62 allow the passage of blood throughplate 60 from within the upper channel shaped region 30. The platesadjacent the fibers are constructed such that each orifice border ischamfered to minimize sharp edges which might damage the hollow fibers.

The diffuser plate 60 bears against the hollow fiber bundle 64 withinupper channel 30. The plate 60 assists in holding the hollow fibers atthe desired pack density of fibers per unit area within the region 30.It is assisted in that purpose by cover 70. The orifices in plate 60allow blood to pass through the bundle 64 from the plate 20 in asubstantially planar manner. This provides optimum exposure of the bloodto fiber surfaces and minimizes the pressure drop across the unit. Italso aids in eliminating potential areas of stagnation which decreasesefficiency and might give rise to clotting.

Orifices 62 (and 102, 140 described below) are preferably no greaterthan 1/2 inches (1.27 cm) and preferably about 3/8 inches in diameter.Larger diameter orifices reduce the ability of the plate to provide packdensity control and will allow the fibers to bulge into the orificesthereby potentially creating void spots in the fiber bundle therebelow.Another disadvantage in fibers bulging into the orifices is thatpinching to close a fiber might occur.

An advantage in providing large diameter orifices of the preferred sizeis that the amount of plate surface area blocking fibers from gasexchange is reduced. By minimizing such fiber-plate contact area theoverall efficiency of the device is improved. The number of orificesshould, therefore, be maximized at the preferred size so long as theoutlet plate and cover 70 remains sufficiently rigid to provide packdensity control.

An outer cover member 70 further encloses the hollow fiber bundle asshown in FIGS. 1, 2, and 4. Cover 70 includes a blood outlet port 72which preferably extends perpendicularly to the fibers acrosssubstantially the entire bundle as shown. Preferably, cover 70 alsoincludes a vent port 74, temperature probe port 76 and a sample port 78.Sample port 78 may include a check valve/breather valve which allows asample to be withdrawn without introducing air into chamber 80. Asshown, cover member 70 defines a chamber 80 above diffuser plate 60. Thespacing between outer cover 70 and diffuser plate 60 is provided for byspacer nodes 82 and maintained in part due to the rigidity of diffuserplate 60. However, the force of maintaining the pack density of thefibers toward the diffuser plate tends to deform the highly perforatedplate toward the cover. Therefore, a plurality of spacer nodes 82 areprovided between the cover and outer plate as shown in FIGS. 1 and 3 tofurther stiffen diffuser plate 60 so as to maintain pack density whileproviding superior diffusion. Cover 70 is preferably provided with agrid of outer ribs to give it greater rigidity, as shown in the FIGS.Because of blood pressure there is a tendency for Cover 70 and plate 60to bow and thereby reduce packing density. Ribs 71 remove this tendency.

The packing density of hollow fiber bundle 64 is specified by thefollowing formula: ##EQU1##

Where "d" represents the outer diameter of the hollow fibers, "n" thenumber of hollow fibers enclosed within the housing, "a" the inner widthof the housing and "b" the inner height of the housing between thediffuser plate 60 and center divider 16.

The preferred packing density is between about 50 and 55%. Packdensities below about 45% at this winding angle show a substantial dropin performance and densities as low as 40% will result in channeling ofblood Pack densities of only 40% at this winding angle often exhibitedvisible channels through which blood is preferentially shunted. Suchshunting prevents that blood from being fully oxygenated and carbondioxide removal is also decreased. If shunting is of a significantportion of the blood, stagnation of the slower flowing blood is morelikely. The preferred pack density described above will change withdifferences of fiber diameter and winding angle. This will be readilydetermined empirically by testing the angle of winding for pack densityof various size fibers.

As shown in FIG. 12 entitled "Outlet p02 vs. Pack Density," in order toobtain a blood outlet oxygen partial pressure of at least 200 mm Hg thepack density should be between about 50 and 55 percent. These resultsare for fibers and winding angles as described above.

FIG. 13, entitled "Pressure Drop vs. Pack Density," shows that thepressure drop through the oxygenator bundle at a pack density between 50and 55 percent is less than 150 mm Hg. Again these results are forfibers and winding angles as described above.

The hollow fibers within the oxygenator section are preferably laid insingle fiber or in groups of fibers such that successive single fiber orgroup of fibers are laid at an angle to the previous fiber or group offibers. After one complete layer is laid into upper channel 30, thepattern is shifted slightly. Each successive layer is laid such that thefibers within the layer cross each other as above. Each layer isslightly shifted in phase from the next. The overall effect is that avery uniform pack density is possible and channels are virtuallyeliminated. FIG. 7 shows an incomplete first layer to illustrate theangles between each successive of another layer of fiber. The crossingfiber arrangement is preferable over parallel fiber packing since itforces the blood into effective, but gentle, transverse mixing withouttraumatizing the blood. Straight, uncrossed fibers packed to a 50-55%density may result in some shunting of blood and provide less mixing andtherefore, less oxygen transfer.

One method of obtaining the preferred criss-crossing arrangement offibers is to wind fibers into the oxygenator section of a plurality ofcores 20 which are arranged around the periphery of a polygonal wheel.For example, such apparatus and procedures are described in U.S. Pat.Nos. 4,267,630, 4,276,687, 4,341,005 and 4,343,668. A reciprocatingfiber guide assembly controls the angle that the fibers are laid intothe cores while the wheel rotates. An optimum angle is about 9 measuredbetween the fiber and edge of a core leg 42 or 44. Steeper angles createlower pack densities. Lower angles create higher pack densities.

During the winding process it is desirable to maintain an "as wound"pack density close to the desired finished pack density. Winding thefibers at a density substantially less than the finished density allowsthe fibers to move so that the center will have significant amount ofundesired air space creating channels. Winding fibers in at a higherpack density than the finished density can create a void space betweenthe top layer of fibers and the diffuser plate 60. As the bundles areremoved from the winding wheel, the fibers can randomly move to fill thevoid space, again jeopardizing the precise spacings of the fiber layers.

The oxygenator diffuser plate 60 is then placed on top of the core andthe fibers are cut with a knife. The perforated plate 60 is tacked ontolegs 40, 42 such as by ultrasonic weld points 68. Plate 60 thereby holdsthe pack density at the desired value while allowing fluid to flow inthe planar manner described previously. The fiber ends may be meltedshut or otherwise sealed prior to end potting. The cores are thenremoved from the wheel for assembly of the outer jackets.

The currently preferred method is to wind the fibers onto a hexagonalwheel to which six cores 20 are attached such that the upper channel 30may receive fiber windings. The actuator has a linear speed of 7.2432inches per second and the wheel has a rotational speed of 50.25 rpm. Thelinear acceleration at reciprocating points is 147 inches per second.The winding width of upper channel 30 is 5.75 inches and the anglebetween fibers is 18.30 degrees. Each layer consists of 184 turns of thewheel. A 0.020 second linear actuator pause is made between each layerto slightly offset each layer.

After the required number of winds have been made, a side pottingcompound 84 is introduced along the contact of the hollow fibers and theface of legs 42, 44 of the core 20. Due to the winding angles employed,the packing density at the center of the contact face tends to be lowerthan desired and channeling is possible. Therefore, a urethane pottingcompound is introduced as a bead projecting several fibers deep alongthe contact edge to eliminate possible channels. An acceptable urethaneside potting compound is available from Caschem, Inc. of Bayonne, N.J.and has a viscosity of about 90,000 cps, marketed as Vorite® 689 andPolycin® 943.

In the preferred form of the invention, using a potting compound in themanner described immediately above, is avoided. It has found that theuse of a potting compound introduces variables that may adversely effectthe entire product and does not necessarily accomplish the intendedpurposes of avoiding channeling as well as is desired. To overcome thepotential drawbacks in using a potting system, the preferred form of theinvention makes use of a construction as is shown in cross-section inFIG. 9. There it will be seen that insert members 84A either precast aspart of the original "H" or alternately formed members that areprebonded to the vertical legs of the "H" have been placed into positionas shown. By the use of such members, the winding as illustrated in FIG.7 and FIG. 1 has a means for insuring a compacting adjacent the oppositeedges of the channel in which the fibers are laid. This in effectprovides less space in those edge regions than in the center of thechannel, thereby bringing about the desired compacting without thenecessity for using a potting compound. It will be readily apparent fromFIG. 7 that due to the criss-crossing in winding there is a regionadjacent each leg or wall that has less density of fiber if a simplerectangular trough is used.

As illustrated in FIG. 9 a generally triangular configuration may beused for the leg or wall. Dependent upon the amount of angle in thecriss-crossing to produce the oxygenation portion of the apparatus, onecan advantageously change the shape of the hypotenuse to reflect abulging area 84B as illustrated in FIGS. 10 and 11 in any of a widevariety of configurations as dictated by the winding configuration.Thus, one is able to obtain the desired packing density and substantialfreedom from channeling as has been previously described with respect tothe use of a potting compound. This is accomplished without the problemassociated with use of potting compounds.

Many configurations of the leg portion can be utilized in accomplishingthe advantages of the invention. In essence, the cross-sectional profileof channel 30 is modified to be incrementally smaller near the legs thanthroughout the major part of the channel.

The need to avoid channeling is less severe in the heat exchangerportion of the apparatus although, even in this instance, the use of aninsert member 132 preattached to the facing 120 can be advantageouslyutilized to insure that with the desired number of winds of heatexchange hollow tube, that a predetermined packing density is alsoachieved with less channeling than would be the case without suchflexibility of construction In the instance of the heat exchangerportion of the apparatus, channeling is of lesser consequence to theoperation of the finished unit than is the case with the oxygenatorportion. Therefore, the more elaborate shaping such as illustrated inFIG. 9 is not deemed necessary.

Following winding, the oxygenator diffuser plate 60 is placed on top ofthe core and tack "welded" to legs 40, 42 by ultrasonic welding. Thenthe fibers are cut with a knife. Diffuser plate 60 thereby maintains thepack density near or at the desired value. The cores are then removedfrom the wheel for assembly of the outer jackets. The fiber ends may bemelted shut or otherwise sealed prior to end potting.

The outer cover 70 is sealed onto the core. Ribs 71 will aid in pressingthe fibers to the ultimately desired packing density. The hollow fiberbundle 64 will ultimately be centrifugally end potted, as will bedescribed below along with the heat exchanger tubes. The end pottingregion is shown in the drawings as reference numeral 90. Because of thehigh packing density, the ends of the fibers are preferably spread outmanually prior to potting to ensure that each fiber is encased withinthe compound. This, of course, gives a reduction in packing densitywithin the potting compound region.

The heat exchange section 14 includes the region defined by lowerchannel 40. Channel 40 is filled with a plurality of substantiallyparallel, liquid impermeable hollow tubes 96. The heat exchange hollowtubes 96 are preferably formed from a polyurethane resin such as B.F.Goodrich Estane 58091. The tubes are much larger than the hollow fibersin the oxygenator, typically being about 0.033 inches (840 microns) inoutside diameter with a wall thickness of about 0.004 inches (102microns). In contrast, a typical oxygenator fiber has an outsidediameter of about 200-450 microns and a wall thickness of less than 50microns. The formation of heat exchanger tubes from polyurethane ratherthan the stainless steel, polyethylene, or polypropylene previously usedrepresents a significant advance. While the efficiency of the heatexchanger is an important design consideration, it is vital that theremust be no leakage. The end seals where polyurethane potting compoundsare used with stainless steel tubes represent potential leakage areas ofthe cooling fluid into the blood.

The use of polyurethane heat exchange tubes with the polyurethane endpotting compounds provides a positive seal which insures that no leakagewill occur. This compatibility with the potting compound greatlyincreases the safety of the product.

The hollow tubes are packed into channel 40 such that channeling isminimized. However, performance of the heat exchanger is not greatlyaffected if some channeling is present. A pack density of between about40% and 60% provides an efficient heat exchanger with an acceptablepressure drop. It is preferred to pack the polyurethane tubes at about a45-55% pack density which provides an efficient unit, low pressure dropand low blood priming volume. The thin walled polyurethane hollow tubesprovide good heat transfer. The efficiency desired is in ensuring thatall of the blood is heated or cooled as desired, not in how much heatexchange fluid is required. The temperature differential between theblood and heat exchange fluid should be low to provide better control.

The heat exchanger tubes are preferably cut and then placed into thechannel rather than wound into the channel. Winding is less preferableas it tends to cause the hollow tubes to bend may cause cracks orbreaks. Additionally, the curvature may allow some tubes ends to be toofar inward after cutting which during end potting which may result inleakage in the device. The hollow tubes are then preferably melted shutat both ends simultaneously into a bundle or may be dipped in wax toclose the tubes for end potting. Although it is preferred to use a legshape that controls the cross-sectional area of channel 40, such as byuse of rectangular wedges 132A, it is also acceptable to introduce sidepotting compound 132 along the interface of the heat exchanger tubes 96with legs 42,44 as shown. Side potting 132 may extend several tubes deepinto the heat exchange bundle and decreases the likelihood of channelingwithin the heat exchanger.

A diffuser plate 100 is preferably attached to the core 20 along legs42, 44 as shown by ultrasonic welding at points 108. Diffuser plate 100includes a plurality of orifices 102 and may be identical to thediffuser plate 60. A cover 110 (preferably ribbed for rigidity) furtherencloses the heat exchanger bundle as shown in FIGS. 1, 3, 5 and 6.Cover 110 includes a blood inlet port 114 and may include a temperatureprobe port 116 and sample port 118.

Although the heat exchanger described above will function adequatelywithout the diffuser plate, the addition of the diffuser plate 100lessens shunting and better maintains the desired pack density of theheat exchanger tubes. This increases the efficiency of the heatexchanger. As in the case of the oxygenator diffuser 60, the heatexchanger diffuser 100 is preferably separated from cover 110 by aplurality of nodes 120. Nodes 120 may be joined to cover 110 anddiffuser 100 thereby defining a chamber 130 therebetween.

Centrifugal end potting is well known in the art and is, for example,shown in U.S. Pat. No. 4,389,363 to Molthop. Suitable potting compoundsare available from Caschem, Inc. of Bayonne, N.J. A polyurethane castingsystem of Caschem, Inc. is described in U.S. Reissue Pat. No. 31,389.After potting, the hollow fibers are reopened by conventional techniquessuch as by slicing through the potted bundle with a sharp knife toexpose the interior of the fibers.

The heat exchanger and previously assembled oxygenator bundle may thenbe end potted at each end with a polyurethane potting compound Thehollow tubes are reopened after potting such as by cutting with a sharpknife. The end potting 135 provides a superior seal which providesmaximum assurance that the seal will not leak.

The core 20 allows the end potting of the heat exchange tubes 96 and theoxygenator fibers 50 to be completed together in one potting. Endpotting tends to be time consuming and eliminating the need for twoseparate end potting procedures represents a very marked improvement.Also, a single step potting reduces the possibility of leakage aroundthe potting edges. As shown in FIG. 8, the end potting 90 of theoxygenator bundle and the end potting 135 of the heat exchanger tubes 96in one step results in a polyurethane dam 137 coextensive with potting90 and 135. This dam 137 isolates the fibers 50 from the tubes 96 andencapsulates the end 10 divider plate 16. It has been found that dam 137prevents the possibility of leakage which might otherwise occur in theabsence of a dam extending in a contiguous manner between the centerdivider and the separate end potting areas.

As shown in FIGS. 1-5, blood outlet port 72 and blood inlet port 114preferably are constructed and arranged such that blood is directedacross substantially the width of the fiber and tube bundles in therespective chambers.

As shown in FIGS. 1 and 3, blood flows from the heat exchanger sectioninto the oxygenator section by passing through perforations 140 incenter divider 16. Center divider 16 is preferably constructed andarranged as described above for diffuser plate 60 and the sameconsiderations apply as to the number and size of perforations 140. Allthree diffuser/dividers preferably have about 62% of their surface arearemoved in the form of perforations.

After the heat exchanger tube bundle and oxygenator hollow fiber bundlehave been end potted and reopened, the device is completed by attachingend caps 160 and 170. Ends caps 160, 170 provide gas and heat exchangemedia inlets and outlets to the open ends of the hollow fiber and tubebundles.

End cap 160 is secured to perimeter of the the cross-sectional end ofcore 20 and to outer jackets 70 and 110 and plastic strip 166. Plasticstrip 166 has projecting lugs 167 which aid in spacing and the formingof dam 137. Alternate construction will have strip 166 formed as anintegral part of center divider 16. In the preferred form in which a dam137 is formed during the single end potting step, a seal is formedbetween a plastic strip 166 which is adhered to dam 137 along the widthof the end potted region caps. A gas inlet 162 of end cap 160 allows gasto contact all of the open oxygenator hollow fiber ends. A heat exchangeoutlet 164 allows heat exchange media leaving the interior of the heatexchanger hollow tubes to exit the device.

End cap 170 is constructed in a similar manner to end cap 160. End cap170 includes a gas outlet 172 which collects gas leaving the open endsof the oxygenator hollow fibers such that gas is exhausted through gasoutlet 172. Outlet 172 is preferably sized to accept either a 1/2" (1.27cm) I.D. tubing set or a 1/4"(0.63 cm) I.D. tubing set inserted into thelumen of outlet 172. Vent port 178 may also be provided as shown. Port172 may be connected to a vacuum source in order to prevent anesthesiagas from escaping into the operating room. A heat exchanger inlet 174provides heat exchange media to each of the heat exchanger hollow tubesthrough their open ends. As in end cap 160, end cap 170 may be sealed toplastic strip 166 such that the open ends of the heat exchanger hollowtubes are isolated from the open ends of the oxygenator hollow fibers.

One may achieve even greater assurance against the possibility ofleakage between the spaces that are desired communication with open endsof the tube bundle and the open ends of the hollow fiber bundle andother undesired regions in the following manner. During the end pottingof the hollow fibers and heat exchange tubes, a mold is used, configuredto shape the perimeter region of the potting compound 90 and 35 to ashoulder 200 around the outer ends of hollow fiber bundle 64 and aroundthe outer ends of hollow tube bundle 96. This is illustrated in FIG. 8.Prior to placing end cap 160 as a closure, 0-rings 201 are placed ontoshoulder 200. The tapered walls of end cap 160 press against 0-rings 201and effectively seal the space communication respectively with theinterior of hollow fibers 50 and tubes 96 from each other as well asscaling the blood flow regions from either the gas passing throughhollow fibers 50 or from the fluid used for heat exchange.

Of course, the seals described previously of the potting compound 90 and35 also prevent undesired leakage.

Blood entering inlet 114 sweeps through chamber 130 and more uniformlycontacts the heat exchanger bundle after passing through the diffuser100. Chamber 130, in conjunction with diffuser 100 provides excellentblood flow distribution to the heat exchanger tubes. Observation of theblood through the outer jacket shows that it swirls in the chamber 130.

The oxygenator construction described above provides an even resistanceto blood flow throughout the oxygenator section 12. Flow vectors aresubstantially equal throughout the fiber bundle 64 which maximizesoxygen transfer by minimizing shunting. The inventive outside perfusiondesign provides a greater surface area for gas transfer and providesbetter mixing. With the invention, it is possible by the mixing actionof the blood in flowing around the fibers to get more red blood cellscloser to blood plasma adhering to the fibers such that oxygen dissolvedin the plasma may reach individual the red blood cells.

At the Association Advancement Medical Instrumentation (AAMI) Standardcondition (blood flow rate=6L/min., inlet gas=100% O₂, venous hemoglobinsaturation=65%, hemoglobin concentration=12 gm%) modified to ahemoglobin saturation=55%, a unit having only 3.8 square meters ofhollow fiber surface area provides oxygen transfer at 450 ml/minute.Utilization of the fibers is maximized while pressure drop and bloodprime volumes are kept at low values.

The design allows the mass production of oxygenators having excellentgas transfer rates with reduced production costs. The heat transferefficiency is well within the recommendations of the AAMI Standards.

Through the use of the unique oxygenation section design, it is possibleto maximize utilization of hollow fibers while minimizing the surfacearea of the hollow fibers. Since hollow fiber stock is expensive, thecost savings alone is an important advantage of the invention. The loweroverall surface area of fibers also decreases the likelihood of plateletand fibrinogen aggregation on the fiber surface. A lower hemolysis rateis also found with the decrease in fiber surface area.

The case, diffuser plates, outer jackets and end caps are all preferablyformed from a non-toxic, biocompatible plastic polycarbonate resins.Suitable for the purpose are the Lexan brand resins of General ElectricCo. Polymers Product Department of Pittsfield, Massachusetts. Lexan 144grade polycarbonate resins are currently preferred.

Oxygenators

If heat exchange is not needed in an integrated unit, the oxygenatorfeatures of the invention may be utilized by providing a core having aU-shaped cross-section. Center divider I6 becomes a replacement fordiffuser plate 100 and is supported in spaced relationship to the outercase by projection. The outer jacket would then be secured to the centerdivider. Of course, the end caps would only need gas inlets and outlets.The oxygenator thus described provides all of the advantages found inthe oxygenator section of the device. It may be used in conjunction withsystems having their own separate heat exchange units if desired.

Heat Exchanger

The heat exchanger section described above for the device may beproduced without an oxygenating section. A heat exchanger may beconstructed by utilizing a core having a U-shaped cross-section suchthat center divider 16 is enclosed within outer jacket 70. As above, theend caps would be modified, in this case to provide heat exchangerinlets and outlets only.

Any application needing heat exchange with the advantages of using thepolyurethane hollow tubes described above may be satisfied by followingthe teachings of the invention. A bundle of polyurethane hollow tubesmay be placed in a case and end potted with a polyurethane end pottingcompound. After end caps are secured a heat exchanger is formed in whichthe interior of the hollow tubes are isolated from the flow paths alongthe outside of the tubes. Heat exchange media may be passed through thelumens or outside the lumens as desired by the application. The heatexchanger may include diffuser plates to increase the distribution offluid over the tubes. The unique combination of polyurethane hollowtubes with the polyurethane end potting compound provides maximalsecurity that there will not be leakage in the device.

Although the device is shown in the figures with a core having anH-shaped cross-section, the advantages of the invention may also beattained with a device in which the heat exchange tubes are generallyperpendicular to rather than parallel to the oxygenator fibers. Such adevice may be made by moving the lower portions of legs 42, 44 below thecenter divider to the other edges of the center divider. In such aconstruction the end caps would need to be separate and two separate endpottings would be required. A somewhat less efficient method of assemblywould result.

In considering the invention it must be remembered that the disclosureis illustrative only and that the scope of the invention is to bedetermined by the appended claims.

WHAT IS CLAIMED IS
 1. A device comprising:a) a housing including anelongated rigid core of generally H-shaped cross-section, the coreincluding opposing side walls, joined to a web, the web of said corebeing perforated with a plurality of orifices substantially throughoutthe width and length of the web, said core defining with said side wallsupper and lower longitudinally extending channels, each channel havingupper and lower edges, the opposing side walls of said upper channelbeing interiorly configured to provide a variable cross-sectionalprofile of channel width between said side walls; b) a bundle comprisingmultiple layers of gas exchange hollow fibers of a composition suitablefor gas exchange, the fibers being disposed substantially longitudinallyin said upper channel and each fiber having two ends c) a bundle of heatexchange hollow tubes impervious to liquid, each tube having aninterior, a first end and a second end, said heat exchange bundle beingdisposed substantially longitudinally in said lower chamber; d) firstand second closure members joined to the opposing side walls at theupper edges of said channels and defining with said channels inlet andoutlet manifold chamber space means outwardly of the outermost layers ofsaid gas exchange fibers and outwardly of the outermost heat exchangetubes of aid heat exchange bundle; e) said tubes and said fibers beingencapsulated at regions near the respective ends thereof with apolymeric material which bonds to said side walls and said closuremembers to define a gas exchange cavity and a heat exchange cavity; f)outlet means in fluid communication with said outlet manifold chamberspace means; g) inlet means in fluid communication with said inletmanifold chamber space means; h) said inlet and outlet chamber spacemeans being constructed and arranged such ,that fluid flowing throughsaid housing will flow in a direction generally transverse to thelongitudinal direction of the gas exchange hollow fibers and heatexchange tubes; i) heat exchange fluid inlet means in fluidcommunication with the interior of the heat exchange hollow tubes at thefirst ends thereof; j) heat exchange fluid outlet means in fluidcommunication with the interior of the heat exchange hollow tubes anddisposed at the second ends of the heat exchange tubes; k) gas exchangeinlet means for providing a gas inlet to the interior of the gasexchange hollow fibers at a first end thereof; and 1) gas exchangeoutlet means for providing a gas outlet for the interior of the gasexchange hollow fibers, said gas exchange outlet means being disposed atthe opposite end of the hollow fibers from the gas exchange inlet means.2. The device of claim 1 wherein first and second diffuser plates arepositioned within said manifold space means and in contact with andextending across the outermost layer of said hollow fibers and saidtubes in each respective channel, said diffuser plates defining aplurality of orifices extending therethrough substantially throughoutthe diffuser plates, each of said diffuser plates being respectivelyspaced from said closure members.
 3. The device of claim 2 wherein saiddiffuser plates are constructed and arranged such that the liquid toundergo gas exchange flowing through said device is distributed acrosssubstantially the entire surface of an inlet side diffuser plate and theliquid to undergo gas exchange moves through said heat exchange bundleand said gas exchange bundle substantially in a planar flow untilexiting through the outlet side diffuser plate.
 4. The device of claim 1wherein the interior configuration of said side walls has a generallytriangular cross-section with the hypotenuse of said triangle having aconcave shape with a radius of about 1.25 inches.
 5. The device of claim1 wherein said gas exchange hollow fibers are arranged within said upperchannel in layers of fibers such that each fiber is generally laid at anangle of between about 8 and 25 degrees from the side wall and eachsucceeding fiber crosses the underlying fiber at an angle of about 18degrees with the cross-points of the fibers being offset from eachother.
 6. The device of claim 5 wherein the angle from the side wall isabout 9 degrees.
 7. The device of claim 5 wherein said hollow fibers arepacked within said channel to a pack density of between about 50 andabout 55%.
 8. The device of claim 1 wherein said heat exchanger inletmeans and outlet means comprise separate manifolds providing fluidcommunication to the interiors of the heat exchange hollow tubes andwherein said gas exchange inlet means and outlet means comprise separatemanifolds providing fluid communication to the interiors of the gasexchange hollow fibers, said manifolds being constructed and arrangedsuch that fluid may not flow between the gas exchange hollow fiberinteriors and the heat exchange hollow tube interiors.
 9. The device ofclaim 8 wherein the encapsulation of the end region of said hollowfibers and said tubes includes a unitary bonding to the encircling wallsto give a gas-tight enclosure.
 10. The device of claim 9 wherein theencapsulating polymeric material surfaces at each end of said tubes andsaid hollow fibers supports resilient O-rings encircling the outermostregions of each end of said encapsulated fibers and said tubes andwherein said gas inlet and outlet means and said fluid inlet and fluidoutlet means each are constructed and arranged to sealingly engage therespective O-rings to provide a gas and liquid-tight seal.
 11. Thedevice of claim 1 wherein said gas exchange hollow fibers are arrangedsuch that each succeeding layer of fibers generally crisscrosses thenext adjacent layer of fibers at an angle of about 9 degrees from thelongitudinal axis of the core.
 12. The device of claim 1 wherein saidgas exchange hollow fibers and said heat exchange hollow tubes arearrayed with their longitudinal axes generally parallel to each other.13. The device of claim 12 wherein the remote end portions of saidhollow fibers and said hollow tubes are encapsulated in a polymericmaterial to provide a gas tight seal to the interior chambers and to oneanother.
 14. The device of claim 1 wherein said first and second closuremeans are held spaced from cover means having a ribbed outer surface forstiffness.
 15. A blood oxygenator comprising:a) an elongated housingdefining first and second opposite end openings, said housing havingfirst and second opposing sides and a top and a bottom and first andsecond closure members over said end openings; said opposing sides beinginteriorly configured to provide a variable cross-sectional profile ofchannel width between said side walls; b) a bundle of hollow fibers forgas exchange being disposed inside said housing and having the ends ofsaid fibers spaced from said end closure members, each fiber having aninlet and an outlet end, each of said fiber inlet ends and each of saidfiber outlet ends being respectively in fluid communication with spacesdefined by said first and second closure member and the ends of saidfibers; c) sealant means encapsulating the exterior end portions of saidhollow fibers adjacent the respective fiber inlet and outlet ends andjoined to the walls, top and bottom to define a blood chamber cavity,the ends of the fibers being open to expose the interior of said fibersto the spaces defined by said end closure member; d) blood inlet meanscommunicating with said blood chamber cavity through said housingbottom; e) blood outlet means communicating with said blood chambercavity through said housing top; f) gas inlet means communicating withthe interior of said hollow fibers at the hollow fiber inlet ends; andg) gas outlet means communicating with the interior of said hollowfibers at the hollow fiber outlet ends.
 16. The device of claim 15wherein the sealant means includes a surface at each end of said hollowfibers supporting resilient 0-rings encircling the outermost ends andwherein said gas inlet means and said gas outlet means are eachconstructed and arranged to sealingly engage the respective 0-rings. 17.The oxygenator of claim 15 wherein said hollow fibers are arrangedwithin said housing in a migrating pattern of crossing layers of hollowfibers, said crossed layers of fibers thereby reinforcing each otheragainst a tendency to move under the hydraulic pressure of flowing bloodand wherein said hollow fibers are packed within said housing at adensity of about 50 to about 55%.
 18. The oxygenator of claim 15 whereinthe interior configuration of said side walls has a generally triangularcross-section wherein the hypotenuse of said triangles has regionsadjacent each end thereof with a convex cross-section.
 19. A hollowfiber-type device having an integral heat exchanger, said devicecomprising:a) an oxygenator section, said oxygenator section including:an elongated rigid core of H-shaped cross section defining an upper andlower longitudinally extending groove in said core, the side walls ofthe upper groove having a generally interior triangular cross-section,the core including a center divider between opposing side walls of thecore, which together define said grooves, said center divider beingperforated with a plurality of orifices substantially throughout thewidth and length of the center divider, a plurality of oxygenationhollow fibers arranged longitudinally in said upper groove, said fibersbeing arranged in layers, each fiber having an inlet end and an outletend, said ends of said hollow fibers left open to the interiors thereofand each fiber crossing over the next at an angle of from about 4 toabout 13 degrees from the longitudinal axis of the core; first andsecond walls supporting said hollow fibers at the respective endsthereof said first and second walls being secured to said core, closuremeans defining with said first and second walls manifold chamber spacemeans at the inlet and outlet ends of said fibers; oxygen inlet meanscommunicating with the open ends of said hollow fibers at the inlet endsthereof; gas outlet means communicating with the open ends of saidhollow fibers at the outlet ends thereof; a first cover means enclosingsaid upper groove side walls and end walls, said first cover meansdefining a chamber above the top most layer of hollow fibers, said firstcover means further including an outlet plate constructed and arrangedso as to contact substantially the entire top most layer of hollowfibers, said outlet plate including a plurality of orificessubstantially throughout the width and length of the outlet plate, saidfirst cover means and outlet plate being constructed and arranged suchthat fluid within said chamber between the first cover means and outletplate may pass to said hollow fibers only through said outlet plateorifices; a blood outlet passage provided in the first cover means, saidpassage being constructed and arranged so as to allow passage of bloodfrom said chamber to the exterior of said device; said hollow fiberswithin the space defined by said core, first and second walls and inletplate being packed to a density of about 50 to about 55 percent; b) aheat exchanger section, said heat exchanger section including aplurality of polymeric hollow tubes arranged side by side longitudinallyin said lower groove of said elongated rigid core and each tube havingan inlet and an outlet end, said ends of said hollow tubes left open tothe interior thereof; third and fourth walls supporting said heatexchanger hollow tubes at the ends thereof, said third and fourth wallsbeing secured to said core; heat exchange closure means defining withsaid walls heat exchanger manifold chambers at the inlet and outlet endsof said heat exchanger tubes, a heat exchange medium inlet meanscommunicating with the open ends of said heat exchange hollow tubes; aheat exchange medium outlet means communicating with the opposite openends of said hollow tubes; a second cover means enclosing said lowergroove side walls and third and fourth walls, said second cover meansdefining a second chamber between an outermost layer heat exchangerhollow tubes from said center divider and said second jacket, saidsecond cover means further including an inlet plate constructed andarranged so as to contact substantially the entire outermost heatexchanger hollow tube layer, said inlet plate including a plurality oforifices substantially throughout the width and length of the inletplate, said second cover means and outlet plate being constructed andarranged such that fluid surrounding said heat exchanger hollow tubesmay pass into said second chamber only through said inlet plateorifices; a blood inlet passage provided in the second cover means, saidoutlet passage being constructed and arranged so as to allow passage ofblood into said second chamber.
 20. The device of claim 19 wherein saidfirst and second walls include a surface at each end thereof supportingresilient 0-rings encircling the outermost ends and wherein said closuremeans at said oxygen inlet means and said gas outlet means areconstructed and arranged to sealingly engage the respective 0-rings. 21.The device of claim 20 wherein said third and fourth walls include asurface at each end thereof supporting resilient 0-rings encircling theoutermost and wherein said closure means at each end are constructed andarranged to sealingly engage the respective 0-rings.
 22. The device ofclaim 19 wherein said core, walls, jackets and inlet and outlet platesare formed from a biocompatible polycarbonate polymer.
 23. The device ofclaim 19 wherein said inlet plate is held in a spaced relationship fromsaid second cover means by a plurality of spacing nodes and said outletplate is held in a spaced relationship from said first cover means by aplurality of spacing nodes.